LED Driver (120526)

Practically the first thing you are taught about LEDs is that they need a constant current power source. Power LEDs are no different they just need more current. At higher current levels the driver circuit efficiency is of critical importance if we are not to squander the energy advantages of LEDs.

The author sent three PCBs, configured for 350 mA each connected to a different colored led (a red, green and blue one).

5V:

Uled[V] Ushunt[V] Pin total

Red 2.156 0.250 5 V x 0.76A

Green 3.452 0.253

Blue 3.108 0.250

12V:

Uled[V] Ushunt[V] Pin total

Red 2.146 0.247 12 V x 0.34A

Green 3.432 0.250

Blue 3.095 0.247

16V:

Uled[V] Ushunt[V] Pin total

Red 2.144 0.246 16 V x 0.27A

Green 3.424 0.246

Blue 3.089 0.243

On all PCBs the shunt resistors are 1 Ω and 2.4 Ω in parallel, so 0.706 Ω

Calculating the efficiency:

5 V 81.6 %

12 V 86 %

16 V 92.7 %

A small single sided PCB was designed (28.87 x 24.75 mm). All components are mounted on top. Wires can be soldered directly to the PCB. Make sure power leds have sufficient cooling otherwise their lifespan will be shortened considerably.